I. Field of the Invention
The present invention relates to fuel injection systems for internal combustion engines and, more particularly, to a cold start fuel injector for such a fuel system.
II. Description of the Prior Art
In internal combustion engines which utilize fuel injection systems, it is conventional to utilize a cold start fuel injector to provide fuel to the engine while the engine is cold. Typically, a single cold start fuel injector supplies fuel to the intake manifold for the engine and thus for all of the engine cylinders.
In order to supply fuel to the cold start injector, the cold start injector has a fuel inlet which is fluidly connected to the fuel rail for the engine. The fuel rail for the engine, in turn, is pressurized by the fuel pump to relatively high pressure, typically 40 psi. This pressurized fuel is supplied via a pulsed valve to the cold start fuel injector nozzle which generates a fuel spray each time the valve is opened. Additionally, secondary air may be provided to the fuel injector nozzle in order to further enhance the atomization of the fuel.
Even the use of secondary air flow through the cold start fuel injector is not sufficient to vaporize the fuel to a level necessary to meet the projected emission regulations for automotive vehicles. Consequently, in order to further enhance vaporization of the fuel, there have been previously known systems which utilize a heater at the outlet from the cold start fuel injector which further enhances fuel vaporization. Such heaters, however, have not proven wholly satisfactory in use.
One disadvantage of these previously known heaters is that the fuel spray from the cold start fuel injector, and particularly, the larger droplets of fuel spray, tend to rapidly cool the heater. This cooling of the heater results in larger fuel droplet size.
Similarly, these previously known cold start fuel injectors utilize relatively short bursts of high pressure fuel to supply fuel to the engine. These high pressure short bursts of fuel also result in larger fuel droplet size and, thus, less efficient fuel combustion.